We suceeded in the preparation of polycrystalline Ca_2FeReO_6 which has a Curie temperature of 540 K, the highest value of all magnetic perovskites investigated up to now. This material has been characterised by X-ray and neutron powder diffraction. We found at 548 K a monoclinic unit cell (space group P2_1/n) with a=5.4366(5) A, b=5.5393(5) A, c=7.7344(5) A, and beta=90.044(4) deg. For low temperatures a phase separation in two monoclinic phases with identical cell volume is observed in neutron scattering. The two phases possess different magnetic structure and coercivity. 57-Fe-Moessbauer spectroscopy measurements show the presence of four different Fe(3+) positions indicating two different phases at room temperature, indistinguishable in the diffraction experiments. The conductivity is thermally activated for all temperatures and no significant magnetoresistivity is observed.
@article{arxiv.cond-mat/0004275,
title = {Magnetic and structural properties of the double-perovskite Ca_2FeReO_6},
author = {W. Westerburg and O. Lang and C. Felser and W. Tremel and M. Waldeck and F. Renz and P. Guetlich and C. Ritter and G. Jakob},
journal= {arXiv preprint arXiv:cond-mat/0004275},
year = {2007}
}
Comments
RevTeX, 8 pages, 12 EPS figures, 5 Tables, submitted to J. Phys.: Condens. Matter